I/O Systems and Subsystems

I/O devices are very important in the computer systems.They provide users the means of interacting with the system. So there is a separate I/O system devoted to handling the I/O devices.

The different Components of the I/O systems are −

I/O Hardware

There are many I/O devices handled by the operating system such as mouse, keyboard, disk drive etc. There are different device drivers that can be connected to the operating system to handle a specific device. The device controller is an interface between the device and the device driver.

A diagram to represent this is −

I/O Application Interface

The user applications can access all the I/O devices using the device drivers, which are device specific codes. The application layer sees a common interface for all the devices.

This is illustrated using the below image −

Most of the devices are either block I/O and character I/O devices. Block devices are accessed one block at a time whereas character devices are accessed one character at a time.

I/O Software

The I/O software contains the user level libraries and the kernel modules. The libraries provide the interface to the user program to perform input and output. The kernel modules provides the device drivers that interact with the device controllers.

The I/O software should be device independent so that the programs can be used for any I/O device without specifying it in advance. For example - A program that reads a file should be able the read the file on a hard disk, floppy disk, CD-ROM etc. without having to change the program each time.